Who am I?

• https://pschmitt.net
• Academics
  • PhD at UCSB
  • Researcher (summers) at ICSI
  • Postdoc then research faculty at Princeton
  • Some other stops… USC, Stanford, UH
• Privacy startup co-founder & CEO, measurement startup COO
• Main focuses
  • Integrating privacy and security into systems that we all use
  • ML for network management
  • Connectivity / privacy in challenging environments

This class

• Too much to cover in one term: survey of important topics
• Course Canvas: https://canvas.calpoly.edu/courses/168889
• Syllabus: https://schmittpaul.github.io/CSC453W26/syllabus.pdf
• Waitlists…
• What OSes do you all run?

Who are you?

• Name / Major / Year
• Where do you identify as your hometown?

How to succeed in this class

• Turn things in on time
• Attend class
  • … on time. Lectures will start at 10 after the hour
    
• Ask questions
  • I’m very flexible about how much we cover this semester
  • I would rather teach less and have everyone understand it
  • Our back-and-forth during class is the one of the few indicators I have of how much you are absorbing
• Talk to me if you are struggling

What are we doing here?

Why take this class

• You are required to do so in order to graduate
• Reality: this is how computers really work, and as a computer scientist or engineer you should know how computers really work
• Ubiquity: operating systems are everywhere and you are likely to eventually encounter them or their limitations
• Beauty: operating systems are examples of mature solutions to difficult design and engineering problems. Studying them will improve your ability to design and implement abstractions

Course progression

• Introduction to operating system abstractions and structures
• Abstracting and multiplexing:
  • CPU: interrupts, context, threads, processes, processor scheduling, thread synchronization, deadlocks
  • Memory: memory layout, address translation, paging and segmentation, address spaces, translation caching, page fault handling, page eviction, swapping
  • File systems and storage: disk scheduling, on-disk layout, files, buffer cache, crash and recovery
  • Security (time permitting)

Questions to consider

• What is an operating system?
• What do they do?
• How did OSes evolve?
• How do the requirements differ for different OSes?

What is an operating system?

OS history - how did we get here?

Types of operating systems

• Desktop
• Time share/Mainframe
• Mobile
• Web
• Real-time
• Embedded
• Virtual Machines

Tl;dr

OSes continue to evolve as environments (i.e., constraints) change

Questions to consider

• What are the main abstractions OSes provide?
• What are the abstraction challenges?

Abstractions

• Abstractions simplify application design by:
  • hiding undesirable properties,
  • adding new capabilities, and
  • organizing information
• Abstractions provide an interface to application programmers that separates policy—what the interface commits to accomplishing—from mechanism—how the interface is implemented.

What are the abstractions?

• CPUs
  • Processes, threads
• Memory
  • Address space
• Disk
  • Files

Example OS abstraction: file systems

• What undesirable properties do file systems hide?
  • Disks are slow!
  • Chunks of storage are actually distributed all over the disk
  • Disk storage may fail!
• What new capabilities do files add?
  • Growth and shrinking
  • Organization into directories, searchability
• What information do files help organize?
  • Ownership and permissions
  • Access time, modification time, type, etc.

Abstraction tradeoffs - discussion

• Identify undesirable properties hidden by, new capabilities added, and info organization provided with these abstractions:
  • Process / threads
  • Address space

Abstraction pros / cons

• Advantages of OS providing abstractions?
  • Allow applications to reuse common facilities
  • Make different devices look the same
  • Provide higher-level or more useful functionality
• Challenges?
  • What are the correct abstractions?
  • How much should be exposed?

OS design requirements - what do we need?

• Convenience, abstraction of hardware resources for user programs
• Efficiency of usage of CPU, memory, etc.
• Isolation between multiple processes
• Reliability, the OS must not fail
• Other:
  • Security
  • Mobility

Questions to consider

• How does the OS manage access to resources?

OS as a resource manager

• Another view: resource manager - shares resources “well”
• Advantages of the OS managing resources?
  • Protect applications from one another
  • Provide efficient access to resources (cost, time, energy)
  • Provide fair access to resources
• Challenges?
  • What are the correct mechanisms?
  • What are the correct policies?

Resources are managed via services

• Program Execution (loading, running, monitoring, terminating)
• Performance (optimizing resources under constraints)
• Correctness (overseeing critical operations, preventing interference)
• Fairness (access to and allocation of resources)
• Error detection & recovery (network partition & media failure)

Services (cont’d)

• Communication (inter-process, software-to-hardware, hardware-to-hardware, system-to-system, wide-area)
• I/O: reading & writing, support for various mediums, devices, performance, and protections
• Data Organization (naming), Services (search) & Protection (access control)
• Security (isolation, enforcement, services, authentication, accounting and logging, trust)
• User interfaces (command-line, GUIs, multiple users)

Each service has challenges and tensions

Example 1: We have limited RAM, and we want to run more programs that can be stored.

• How do we allocate space?
• Who stays?
• Who goes?
• What if we’re wrong?
• What if the system is under extremely heavy load?
• Is there a way to predict the future?

Each service has challenges and tensions

Example 2: We have two process (producer / consumer); how do they communicate?

• Message passing? Shared memory?
• How do they synchronize?
  • How to we prevent over-production? Over-consumption?
  • Context-switching?